1. Field of the Invention
The invention relates to a process for producing a fuel cell stack by stacking the fuel cells into a stack, and joining the fuel cell stack as the assembled fuel cell stack is heated and compressed.
Furthermore, the invention relates to a device for producing a fuel cell stack, especially a device for carrying out the process of the invention, with a heating means for heating the assembled fuel cell stack, and a means for compressing the assembled fuel cell stack.
2. Description of Related Art
For example, known SOFC fuel cell stacks (SOFC=“solid oxide fuel cell”) generally comprise several fuel cell elements with seals located between the fuel cell elements and a pair of end plates and current collector plates. These fuel cell stacks are produced by known production processes, for example, as follows. First of all, the fuel cells are stacked into a stack cold. In doing so, the anode sides of the fuel cells are still in the unreduced state (for example, NiO instead of Ni). Compressible seals are still uncompressed and glass seals, such as, for example, glass paste or glass solder, are still unmelted, i.e., green. In the known production processes, the assembled fuel cell stack is then heated in a furnace until the glass paste or the glass solder melts. Here, the fuel cell stack is compressed under a mechanical load so that the seals melt and seal. At the same time or subsequently, a reducing gas is delivered into the anode space of the fuel cell stack, for example, hydrogen, by which the anode is reduced, for example, from NiO to Ni. Optionally, the mechanical load continues during the reduction process, i.e., further compression of the fuel cell stack takes place in order to compensate for the reduction in the thickness of the fuel cells during shrinkage.
For example, U.S. Pat. No. 4,615,107 discloses one possibility for compression of an assembled fuel cell stack.
One problem in the known processes and devices for producing fuel cell stacks is that the joining of the fuel cell stack takes placed uncontrolled and without the possibility of being able to intervene in the process, for which reason scrap rates are high. Furthermore, for example, the fuel cell stack can only be checked for gas-tightness after completion of the joining process.